The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and the lens. The lens is held in place within the posterior chamber of the eye by a membrane known as the capsular bag or posterior capsule, immersed in the aqueous humor. The shape of the lens and the refractive index of the lens relative to the aqueous humor determine where light rays are focused onto the retina.
When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial intraocular lens (IOL). Cataractous lenses are often removed by a surgical technique called phacoemulsification. During this procedure, an opening is made in the anterior side of the capsular bag, a thin membrane enclosing the natural lens. A thin phacoemulsification cutting tip is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquefies or emulsifies the lens so that the lens may be aspirated out of the eye. The diseased lens, once removed, is replaced by an artificial lens.
In the natural lens, multifocality of distance and near vision is provided by a mechanism known as accommodation. The natural lens, early in life, is soft and contained within the capsular bag. The bag is suspended from the ciliary muscle by the zonules. Relaxation of the ciliary muscle tightens the zonules, and stretches the capsular bag. As a result, the natural lens tends to flatten. Tightening of the ciliary muscle relaxes the tension on the zonules, allowing the capsular bag and the natural lens to assume a more rounded shape. In this way, the natural lens can be focused alternatively on near and far objects. As the lens ages, it becomes harder and is less able to change shape in reaction to the tightening of the ciliary muscle. This makes it harder for the lens to focus on near objects, a medical condition known as presbyopia. Presbyopia affects nearly all adults over the age of 45 or 50.
When a cataract or other disease requires the removal of the natural lens and replacement with an artificial intraocular lens (“IOL”), the IOL used to replace the natural lens has often been a monofocal lens. These lenses do not change power in response to the movement of the capsular bag, requiring that the patient use a pair of spectacles or contact lenses for near vision. However, there are several examples in the prior art of bladder or bag-like intraocular lenses that consist of an outer flexible skin filled with a viscous gel. The resulting lens completely fills the capsular bag and is very soft and pliable, much like the natural lens. See for example, U.S. Pat. No. 4,373,218 (Schachar), U.S. Pat. No. 4,585,457 (Kalb), U.S. Pat. No. 4,685,921 (Peyman), U.S. Pat. No. 4,693,717 (Michelson), U.S. Pat. No. 5,275,623 (Sarfarazi), U.S. Pat. No. 4,822,360 (Deacon), U.S. Pat. No. 5,489,302 (Skottun) and U.S. Pat. No. 6,217,612 (Woods). But in order to provide accommodation, movement of the ciliary muscle must be adequately transmitted to the lens system through the capsular bag, and none of these references disclose a mechanism for ensuring that there is a tight connection or fixation between the capsular bag and the lens system.
Therefore, a need continues to exist for a safe and stable accommodative intraocular lens system and method for implantation that provides accommodation over a broad and useful range.